I'm not a coder, but many of us have CUDA-enabled GPUs that aren't being stressed much at all (my load temp is in the high 80s, PCSX2 never heats it past 70C), so maybe there's some extra processing power in there.

Maybe there is, but we'll never know.
The thing is that doing anything noteworthy on CUDA would require a lot of rewriting and thinking.
And even if that resulting code worked (not sure!), it may be too slow to be usuable.
Data transfer from and to GPU is slow, and we can't say how that would affect it.

All in all, I'm sure no one will try to use it.
(Well, except maybe a gs plugin author..)